Transmitter and receiver for frequency domain equalization

ABSTRACT

A transmitter and/or receiver for performing frequency domain equalization is provided. A transmitter includes a pilot position determination unit for determining positions for inserting pilots in a frequency domain based on frequency spectrums of data, and a pilot insertion unit for inserting the pilots between the frequency spectrums of the data according to the determined positions for inserting the pilots.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) of a KoreanPatent Application No. 10-2008-0031742, filed on Apr. 4, 2008 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The following description relates to a wireless communication system,and more particularly, to a transmitter and/or receiver for performingfrequency domain equalization.

BACKGROUND

Generally, users and service providers require communication services beavailable regardless of time and location, and with a high quality at alow cost. There are provided an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, a Single Carrier Frequency DomainEqualization (SC-FDE) scheme, and the like to achieve a high speed datatransmission rate.

For a receiver for performing frequency domain equalization to equalizedistortion of a signal transmitted from a transmitter through a wirelesschannel, a wireless channel state may be required to be estimated by thereceiver. In this case, the receiver may estimate the wireless channelstate based on pilots transmitted from the transmitter.

The transmitter may transmit the pilots to the receiver using variousmethods.

As an example, a transmitter may decrease the number of data to betransmitted to a receiver, so as to insert a number of pilots in afrequency domain. For example, the transmitter may decrease the numberof data up to an ‘x’ number of pilots in a frequency domain to insertthe ‘x’ number of pilots. In this case, spectral efficiency may bedeteriorated since the number of data to be transmitted to the receiveris decreased to insert the number of pilots.

As another example, a transmitter may eliminate data in a frequencydomain and insert pilots in positions corresponding to the eliminateddata. In this case, distortion may exist in a time domain signal sincethere are eliminated data in the frequency domain.

Accordingly, there is needed a technique that may reduce the distortionof a signal without deteriorating efficiency of a frequency.

SUMMARY

In one general aspect, a transmitter comprises a pilot positiondetermination unit which determines positions for inserting pilots in afrequency domain based on frequency spectrums of data, and a pilotinsertion unit which inserts the pilots between the frequency spectrumsof the data according to the determined positions for inserting thepilots.

The pilot position determination unit may determine the positions forinserting the pilots based on distortion strength of the data.

The pilot position determination unit may determine the positions forinserting the pilots based on the frequency spectrums of the data so asto minimize distortion strength of the data.

The pilot position determination unit may extract the frequencyspectrums of the data according to a predetermined frequency interval,and determine the positions for inserting the pilots based on theextracted frequency spectrums of the data so that the distortionstrength of the data is a minimum.

The pilot insertion unit may eliminate target elimination spectrumscorresponding to the determined positions for inserting the pilots fromamong the frequency spectrums of the data, and insert the pilotsaccording to the determined positions for inserting the pilots.

The pilot insertion unit may insert the pilots between the frequencyspectrums of the data according to the determined positions forinserting the pilots with a predetermined frequency interval.

The transmitter may further comprise an inverse discrete Fouriertransformer (IDFT) which transforms the frequency spectrums of the dataand the inserted pilots into a time domain signals.

The transmitter may further comprise a cyclic shifter whichcyclic-shifts the frequency spectrums of the data and the insertedpilots so that at least one target pilot of the pilots exists in apredetermined position.

In another general aspect, a receiver for performing frequency domainequalization comprises a signal receiving unit which receives a signaltransmitted from a transmitter via a channel, a first discrete Fouriertransformer (DFT) which transforms the received signal into a firstfrequency domain signal, the first frequency domain signal includingfrequency spectrums of data and pilots, a channel estimator whichascertains positions of the pilots with respect to positions of thefrequency spectrums of the data using a channel frequency response beingcalculated based on the pilots, and estimates a frequency response ofthe channel, and a frequency domain equalizer which performsequalization with respect to the first frequency domain signal based onthe estimated frequency response of the channel.

The receiver may further comprise a detector which detects the data in atime domain according to an iterated detecting scheme.

The detector may comprise an inverse discrete Fourier transformer (IDFT)which transforms an output of the frequency domain equalizer into a timedomain signal, a decision unit which makes a decision with respect to anoutput of the IDFT, a second DFT which transforms an output of thedecision unit into a frequency domain signal, and an adder whichprovides a signal being generated by adding an output of the second DFTand the output of the frequency domain equalizer to the IDFT.

The detector may iteratively detect the data up to a predeterminednumber of times.

The channel estimator may analyze, in a time domain, a channel frequencyresponse being calculated based on the data and a channel frequencyresponse being calculated based on the pilots to ascertain the positionsof the pilots, and estimate the frequency response of the channel.

The channel estimator may ascertain the positions of the pilots based ona dispersion of a first time domain response and a dispersion of asecond time domain response, and estimates the frequency response of thechannel, wherein the first time domain response is a time domainrepresentation of a channel frequency response being calculated based onthe data and the second time domain response is a time domainrepresentation of the channel frequency response being calculated basedon the pilots.

In still another general aspect, a receiver for performing frequencydomain equalization comprises a signal receiving unit which receives asignal transmitted from a transmitter via a channel, a first discreteFourier transformer (DFT) which transforms the received signal into afirst frequency domain signal, the first frequency domain signalincluding frequency spectrums of data and pilots, and the frequencyspectrums of the data and the pilots being cyclic-shifted so that atleast one target pilot of the pilots exists in a predetermined position,a frequency domain equalizer which estimates the channel based on thepilots and equalizes the first frequency domain signal based on theestimated channel, a first inverse discrete Fourier transformer (IDFT)which transforms an output of the frequency domain equalizer into a timedomain signal, a cyclic shift determination unit which determines howmuch the frequency spectrums of the data and the pilots arecyclic-shifted, based on an output of the first IDFT, a phase adjustingunit which adjusts a phase of the output of the first IDFT based on thedetermination result, and a decision unit which makes a decision withrespect to the data using an output of the phase adjusting unit.

The receiver may further comprise a second DFT which transforms anoutput of the decision unit into a frequency domain signal, an inversecyclic shifter which cyclic-shifts the output of the frequency domainequalizer as much as the frequency spectrums of the data and the pilotshave been cyclic-shifted, in an inverse direction to that of thefrequency spectrums of the data and the pilots, an adder which adds anoutput of the inverse cyclic shifter and an output of the second DFT,and a second IDFT which transforms an output of the adder into a timedomain signal and provides the transformed time domain signal to thedecision unit.

In yet another general aspect, a signal transmission method forperforming frequency domain equalization comprises determining positionsfor inserting pilots in a frequency domain based on frequency spectrumsof data, and inserting the pilots between the frequency spectrums of thedata according to the determined positions for inserting the pilots.

The determining of the positions for inserting the pilots may comprisecalculating distortion strength of the data based on the frequencyspectrums of the data where the pilots are inserted, and determining thepositions for inserting the pilots so that the calculated distortionstrength is a minimum.

The method may further comprise cyclic-shifting the frequency spectrumsof the data and the inserted pilots so that at least one target pilot ofthe pilots exists in a predetermined position.

Other features will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theattached drawings, discloses exemplary embodiments of the invention

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a transmitter and a receiver accordingto an exemplary embodiment.

FIG. 2 is a diagram illustrating a transmitter for performing frequencydomain equalization according to an exemplary embodiment.

FIG. 3 is a diagram illustrating a receiver for performing frequencydomain equalization according to an exemplary embodiment.

FIG. 4 is a diagram illustrating a transmitter for performing frequencydomain equalization according to another exemplary embodiment.

FIG. 5 is diagram illustrating a receiver for performing frequencydomain equalization according to another exemplary embodiment.

FIG. 6 is flowchart illustrating a method for transmitting a signal forperforming frequency domain equalization according to an exemplaryembodiment.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The elements maybe exaggerated for clarity and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the media, apparatuses, methodsand/or systems described herein. Accordingly, various changes,modifications, and equivalents of the systems, methods, apparatusesand/or media described herein will be suggested to those of ordinaryskill in the art. Also, description of well-known functions andconstructions are omitted to increase clarity and conciseness.

FIG. 1 illustrates a transmitter 110 and a receiver 120 according to anexemplary embodiment.

Referring to FIG. 1, a wireless channel is formed between thetransmitter 110 and the receiver 120. The receiver 120 estimates thewireless channel state based on pilots transmitted from the transmitter110. Also, the receiver 120 performs equalization with respect toreceived signals in a frequency domain based on the estimated wirelesschannel state.

The transmitter 110 may transmit signals in each block to the receiver120, and a transmission length of a single block may be N in a timedomain.

The single block may include an Np number of pilot signals. In thiscase, the pilots {C_(k)}_(k=0) ^(N) ^(p) ⁻¹ in the frequency domaintransmitted from the transmitter 110 may be represented by,

$\begin{matrix}{C_{k} = \left\{ \begin{matrix}{\mathbb{e}}^{{{j\pi}\;{{rk}^{2}/N_{p}}},} & {{for}\mspace{14mu}{even}\mspace{14mu} N_{p}} \\{{{\mathbb{e}}^{{j\pi}\;{{rk}{({k + 1})}}}/N_{p}},} & {{for}\mspace{14mu}{odd}\mspace{14mu} N_{p}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where r indicates a relatively prime of Np.

It may be desirable to arrange pilots in a suitable position in afrequency domain. As an example, it is assumed that specific frequencyspectrums of frequency spectrums are randomly eliminated, and pilots arearranged in place of the eliminated specific frequency spectrums. Inthis case, a transmission signal, which is generated throughtransformation into a time domain after the pilots are arranged, may bedistorted, the transmission signal being generated by transformingoriginal data into a time domain due to the eliminated frequencyspectrums. Also, where pilots are additionally arranged to frequencyspectrums of data, spectral efficiency may be deteriorated since anumber of data being transmitted is decreased. Therefore, according toan aspect, there is provided a method of reducing distortion of a signalwithout deteriorating the spectral efficiency.

Determining Positions of Pilots

1) An exemplary method:

Data in a time domain included in a single block with a transmissionlength N are {s_(n)}_(n=0) ^(N−1), and {s_(n)}_(n=0) ^(N−1) may betransformed into frequency spectrums {S_(k)}_(k=0) ^(N−1) via a discreteFourier Transformation. Also, {C_(k)}_(k=0) ^(N) ^(p) ⁻¹ may be arrangedwith a predetermined frequency interval.

In this case, Φ_(m) and Ψ_(m) may be defined as described in Equation 2.

$\begin{matrix}{{\Phi_{m} = \left\lbrack {S_{m},S_{M + m},S_{{2M} + m},\ldots\;,S_{{{({N_{p} - 1})}M} + m}} \right\rbrack^{T}}{{\Psi_{m} = \left\{ {m,{M + m},\ldots\;,{{\left( {N_{p} - 1} \right)M} + m}} \right\}},{0 \leq m < {M.}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, it is assumed that a time domain signal with respect to a signalwhose frequency spectrums Φ_(m) corresponding to a position of Ψ_(m)from among frequency spectrums of data is eliminated is {x′_(m,n)}_(n=0)^(N−1). In this case, distortion strength between an original signal anda signal being actually transmitted may be represented by,|s _(n) −x′ _(m,n)|².  [Equation 3]

Therefore, a position of the first pilot of the Np number of pilots maybe determined via Equation 4. Where the position of the first pilot isdetermined, all positions of the Np number of pilots may be determinedsince a frequency interval of neighboring pilots is M.

$\begin{matrix}\begin{matrix}{d_{o} = {\arg{\min\limits_{m}{\sum\limits_{n = 0}^{N - 1}{{s_{n} - x_{m,n}^{\prime}}}^{2}}}}} \\{= {\arg{\min\limits_{m}{\sum\limits_{n = 0}^{N - 1}{{\frac{1}{\sqrt{N}}{\sum\limits_{k \in \Psi_{m}}{S_{k}{\mathbb{e}}^{j\frac{2\;\pi\;{nk}}{N}}}}}}^{2}}}}} \\{= {\arg{\min\limits_{m}{\left( {{\sum\limits_{k \in \Psi_{m}}{S_{k}}^{2}} + {\frac{1}{N}{\underset{n = 0}{\sum\limits^{N - 1}}{\sum\limits_{k \in \Psi_{m}}{\sum\limits_{\underset{l \neq k}{l \in \Psi_{m}}}{S_{k}S_{l}^{*}{\mathbb{e}}^{j\frac{2\pi\; n{({k - l})}}{N}}}}}}}} \right).}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

After the positions of the pilots are determined, pilots may be arrangedin place of the frequency spectrums of the data. Consequently,representation in a frequency domain of a transmission signal X may berepresented by,X=[S ₀ , . . . , S _(d) _(o) ⁻¹ , C ₀ , . . . , S _(M+d) _(o) ⁻¹ , C ₁ ,. . . , S _(N−1)]^(T).  [Equation 5]

Referring to the Equation 5, S_(d) _(o) and S_(M+d) _(o) are eliminatedand C₀ and C₁ are inserted in their place.

Also, X may be transformed into {x_(n)}_(n=0) ^(N−1) via an inversediscrete Fourier transform (IDFT). Consequently, it may be ascertained{x_(n)}_(n=0) ^(N−1) is a signal which includes pilots and minimizesdistortion strength of {s_(n)}_(n=0) ^(N−1).

2) Cyclic Shift:

Elements included in X may be left cyclic-shifted up to d_(o) number oftimes, and X may be transformed into X₂. That is, X₂ may be representedby,X ₂ =[C ₀ , . . . , S _(M+d) _(o) ⁻¹ , C ₁ , . . . , S _(N−1) , S ₀ , .. . , S _(d) _(o) ⁻¹]^(T).  [Equation 6]

That is, X may be cyclic-shifted so that C₀ becomes the first frequencyelement of X₂. In this case, the receiver 120 may detect pilots byascertaining a number of times X is cyclic-shifted and a direction X iscyclic-shifted to. Here, C₀ may not be required to be a first frequencyelement of X₂, and a position of C₀ in X₂ may depend on an establishmentscheme.

Detection of Pilots

The transmitter 110 may insert pilots according to the above describedexemplary method, and transmit a transmission signal in a time domain tothe receiver 120. According to an exemplary embodiment, the receiver 120detects the pilots to estimate a channel state and to perform frequencydomain equalization.

1) Where the transmitter 110 arranges pilots using the exemplary method,and transmits a transmission signal X in a frequency domain:

The receiver 120 may need to ascertain positions of pilots in afrequency domain. Where the transmitter 110 transmits informationassociated with d_(o) to the receiver 120, the receiver 120 mayascertain the positions of the pilots in the frequency domain based onthe information associated with d_(o). However, the receiver 120 mayascertain the positions of the pilots in the frequency domain withoutthe information associated with d_(o).

Frequency representation of the received signal in the receiver 120 maybe represented by,

$\begin{matrix}{R_{k} = \left\{ \begin{matrix}{{{H_{k}C_{k}} + V_{k}},} & {{k\left( {{mod}\mspace{14mu} M} \right)} = d_{o}} \\{{{H_{k}S_{k}} + V_{k}},} & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

where H_(k) indicates a channel frequency response of a K^(th) carrier,and V_(k) indicates a zero-mean complex additive white Gaussian noise.Here, Equation 8 may be provided:Λ_(kM+m) =R _(kM+m) /C _(k)Λ_(m)

[Λ_(m), Λ_(M+m), Λ_(2M+m), . . . , Λ_((N) _(p) _(−1)M+m)]^(T)

where Λ_(m) may be represented in a time domain by,{λ_(0,n)}_(n=0) ^(N) ^(p) ⁻¹, . . . , {λ_(M−1,n)}_(n=0) ^(N) ^(p)⁻¹.  [Equation 9]

Where m=d_(o), it is considered that the receiver 120 has performedchannel estimation normally in a frequency domain. However, where ism≠d_(o), it is considered that the receiver 120 has not performed thechannel estimation normally in a frequency domain. Equation 10 may berepresented by a central limit theorem.

$\begin{matrix}{\lambda_{m,n} \approx \left\{ \begin{matrix}{{\sqrt{N_{p}}h_{n}},} & {{{if}\mspace{14mu} m} = d_{o}} \\{{N\left( {0,\sigma_{s}^{2}} \right)},} & {{otherwise}.}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

where an average of N(0,σ_(s) ²) is 0, σ_(s) ² is dispersion.

The receiver 120 may ascertain positions of pilots based on dispersionof amplitudes of each of {_(0,n)}_(n=0) ^(N) ^(p) ⁻¹, . . . ,{λ_(M−1,n)}_(n=0) ^(N) ^(p) ⁻¹. In this case, the receiver 120 mayestimate d_(o) using Equation 11.

$\begin{matrix}{{\overset{\_}{\lambda}}_{m} = {\frac{1}{N_{p}}{\sum\limits_{n = 0}^{N_{p} - 1}{{\lambda_{m,n}}\mspace{14mu}{\hat{d}}_{o}\arg{\max\limits_{m}{\frac{1}{N_{p}}{\sum\limits_{n = 0}^{N_{p} - 1}{\left( {{\lambda_{m,n}} - {\overset{\_}{\lambda}}_{m}} \right)^{2}.}}}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

As described above, the receiver 120 may estimate d_(o,) and ascertainthe positions of the pilots. Also, the receiver 120 may estimate achannel state based on the pilots, and may perform equalization in afrequency domain using the estimated channel state.

2) Where the transmitter 110 transmits X₂:

Where the transmitter 110 transmits X₂, the receiver 120 may ascertainthat a first frequency element of X₂ is C_(0.) In this case, wherefrequency spectrums of data included in X₂ are cyclic-shifted up tod_(o) number of times, the receiver 120 may be need to ascertain d_(o)number of times. Also, the receiver 120 may correctly detect data bycyclic-shifting the received signal up to d_(o) number of times in aninverse direction of the frequency spectrums of data included in X₂being cyclic-shifted.

A signal having performed equalization in a frequency domain by thereceiver 120 may be represented by,

$\begin{matrix}{Y_{k} = \left\{ \begin{matrix}{0,} & {{{k\left( {{mod}\mspace{14mu} M} \right)} = 0},} \\{{{\frac{{\hat{H}}_{k}^{*}}{{{\hat{H}}_{k}}^{2} + \sigma_{v}^{2}}R_{k}} = {W_{k}R_{k}}},} & {{otherwise},}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

A ‘Cyclic shift’ in a frequency domain may correspond to a ‘phase shift’in a time domain. That is, d_(o) may be estimated based on a time domainsignal y_(n) corresponding to Y_(k) as below:

$\begin{matrix}{{\hat{d}}_{o} = {\arg{\min\limits_{m}{\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{\left\lbrack {\min\limits_{a_{i} \in X}{{{y_{n}{\mathbb{e}}^{j\frac{2\pi\;{mn}}{N}}} - a_{i}}}^{2}} \right\rbrack.}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

Consequently, d_(o) may be estimated via the Equation 13, and based onthe estimated d_(o), a number of times frequency spectrums arecyclic-shifted may be ascertained, so as to correctly detect data in atime domain.

Restore Distorted Signal

The receiver 120 according to an exemplary embodiment may detect datausing an iterated detecting scheme. That is, data detected in a timedomain may be distorted due to frequency spectrums which have beeneliminated to insert pilots. However, the receiver 120 may recover thefrequency spectrums which have been eliminated to insert pilots usingthe data detected in the time domain, and may repeatedly use therestored frequency spectrums to detect data in a time domain. In thiscase, the receiver 120 may recover the frequency spectrums which havebeen eliminated to insert pilots by iterating the above describedoperations.

Here, the operations of the receiver 120 may be represented by,

$\begin{matrix}{{\overset{\sim}{S}}_{k}^{(i)} = \left\{ \begin{matrix}{{\hat{S}}_{k}^{({i - 1})},} & {{k\left( {{mod}\mspace{14mu} M} \right)} = {\hat{d}}_{o}} \\{{\overset{\sim}{S}}_{k}^{(0)},} & {{otherwise}.}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Where i is 0, {tilde over (S)}_(k) ^((i)) is a signal after equalizationis performed in a frequency domain. Where i is larger than 0, {tildeover (S)}_(k) ^((i)) is representation in a frequency domain of arestored signal. Also, data are determined in a time domain where anumber of times of iterations is i−1, and the determined data aretransformed into a signal Ŝ_(k) ^((i−1)) in a frequency domain.

FIG. 2 illustrates a transmitter for performing frequency domainequalization according to an exemplary embodiment.

As illustrated in FIG. 2, the transmitter for performing frequencydomain equalization comprises a data transformation unit 210, a discreteFourier transformer (DFT) 220, a pilot position determination unit 230,a pilot insertion unit 240, and an inverse discrete Fourier transformer(IDFT) 250.

The data transformation unit 210 transforms information bits accordingto various transformation schemes. Outputs of the data transformationunit 210 are referred to as {s_(n)}.

The DFT 220 transforms the data {s_(n)} into frequency spectrums{S_(k)}.

The pilot position determination unit 230 determines positions forinserting pilots {C_(k)} in a frequency domain based on the frequencyspectrums {S_(k)} of data. The pilot position determination unit 230 maycalculate distortion strength of data as described above, and determinethe positions for inserting the pilots {C_(k)} so that the calculateddistortion strength may be a minimum. In this case, since frequencyintervals between the pilots {C_(k)} are uniform, the pilot positiondetermination unit 230 may determine the positions of all pilots bydetermining d_(o) for the first pilot.

The pilot insertion unit 240 are provided with d_(o) and {X′_(k)} fromthe pilot position determination unit 230. The pilot insertion unit 240eliminates frequency spectrums which correspond to positions forinserting pilots from among the frequency spectrums of data, and insertsthe pilots {C_(k)} between the frequency spectrums {X′_(k)} of the data.Once the pilots {C_(k)} are inserted between the frequency spectrums ofthe data{X′_(k)}, {X_(k)} is generated.

The IDFT 250 transforms the {X_(k)} into a time domain signal {x_(n)},and the time domain signal {x_(n)} is transmitted to the receiver 120via an antenna.

FIG. 3 illustrates a receiver for performing frequency domainequalization according to an exemplary embodiment.

As illustrated in FIG. 3, the receiver comprises a signal receiving unit310, a first DFT 320, a channel estimator 330, a frequency domainequalizer 340, an IDFT 350, a decision unit 360, a second DFT 370, andan adder 380.

In the exemplary embodiment of FIG. 3, it is assumed that a transmittertransmits a signal being generated by inserting pilots between frequencyspectrums of data without cyclic-shifting the pilots between thefrequency spectrums of the data.

The signal receiving unit 310 receives a signal transmitted from thetransmitter via a formed channel between the receiver and thetransmitter.

The first DFT 320 transforms the received signal into a first signal ina frequency domain. In this case, the first signal may include frequencyspectrums of data and pilots. The pilots exist in positions of partialfrequency spectrums of the frequency spectrums of the data, which areoriginally scheduled to be transmitted. However, the partial frequencyspectrums may not be included in the first signal. But, the partialfrequency spectrums may be recovered using an iterated detecting scheme.

The channel estimator 330 ascertains the positions of the pilots withrespect to the positions of the frequency spectrums of the data bycomparing a channel frequency response being calculated based on pilotswith a channel frequency response being calculated based on data. Thechannel estimator 330 detects the pilots based on the ascertainedpositions of the pilots, and estimates a frequency response of achannel.

The frequency domain equalizer 340 performs equalization in a frequencydomain with respect to the first signal based on the estimated frequencyresponse of the channel.

Although not illustrated in FIG. 3, a detector detects data in a timedomain using an iterated detecting scheme. The detector may include theIDFT 350, the decision unit 360, the second DFT 370, and the adder 380.

Where a number of times of iterations is 0, the IDFT 350 transforms{{tilde over (S)}_(k)} into a time domain signal {{tilde over (s)}_(n)}.

The decision unit 360 determines {{tilde over (s)}_(n)} using, forexample, a maximum likelihood detection scheme.

The second DFT 370 transforms the determined {{tilde over (s)}_(n)} intoa frequency domain signal {Ŝ_(k)}.

The adder 380 provides the IDFT 350 with a new signal {Ŝ_(k)}, which isgenerated by adding {Ŝ_(k)}, to an output of the frequency domainequalizer 340.

Consequently, the detector including the IDFT 350, the decider 360, andthe second DFT 370, and the adder 380 may perform the above detectionoperation up to a predetermined number of times so as to recover adistorted signal which is distorted due to the frequency spectrums ofthe eliminated data.

FIG. 4 illustrates a transmitter for performing frequency domainequalization according to another exemplary embodiment.

As illustrated in FIG. 4, the transmitter for performing frequencydomain equalization comprises a data transformation unit 410, a DFT 420,a pilot position determination unit 430, a pilot insertion unit 440, acyclic-shifter 450, and an IDFT 460.

Operations of the data transformation unit 410, the DFT 420, the pilotposition determination unit 430, a pilot insertion unit 440, and theIDFT 460 may be identical to that described above regarding theoperations in FIG. 2.

The cyclic shifter 450 left cyclic-shifts an output of the pilotinsertion unit 440 up to d_(o) number of times in a frequency domain.Consequently, a first element of an output {X_(k)} of the cyclic-shifter450 becomes a first pilot.

In this case, a receiver may not be required to additionally perform anoperation for ascertaining the positions of the pilots since thereceiver may know that the first element of the output {X_(k)} is thefirst pilot. The receiver may ascertain the number of times frequencyspectrums of data are cyclic-shifted by ascertaining d_(o).

FIG. 5 illustrates a receiver for performing frequency domainequalization according to another exemplary embodiment.

As illustrated in FIG. 5, the receiver for performing frequency domainequalization comprises a signal receiving unit 511, a first DFT 512, achannel estimator/frequency domain equalizer 513, a first IDFT 514, acyclic shift determination unit 515, a phase adjusting unit 516, aninverse cyclic shifter 517, an adder 518, a second IDFT 519, a secondDFT 520, and a decision unit 521.

The signal receiving unit 511 receives a signal transmitted from atransmitter via a channel.

The first DFT 512 transforms the received signal into a first signal{R_(K)} in a frequency domain. In this case, the first signal includesfrequency spectrums and pilots, and the frequency spectrums and thepilots are cyclic-shifted so that at least one target pilot of thepilots exists in a predetermined position. Here, for convenience ofexplanation, it is assumed that a target pilot is a first pilot of thepilots, and the predetermined position is a position of a firstfrequency element of the first signal {R_(K)}.

The frequency domain equalizer 513 estimates a channel state based onthe pilots, and performs equalization with respect to the first signal{R_(K)} in a frequency domain using the estimated channel. In this case,an output of the frequency domain equalizer 513 is {Y_(K)}.

The first IDFT 514 transforms the output {Y_(K)} of the frequency domainequalizer 513 into a time domain signal {y_(n)}.

The cyclic-shift determination unit 515 determines the number of timesthe frequency spectrums of data and pilots are cyclic-shifted based onan output of the first IDFT 514. Here, since it is assumed that thepredetermined position is the position of the first frequency element ofthe first signal, it may be ascertained that the frequency spectrums ofdata and the pilots are left cyclic-shifted up to d_(o) number of times.

The phase adjusting unit 516 adjusts a phase of an output of the firstIDFT 514 based on the ascertaining result in the cyclic shiftdetermination unit 515. This is because a ‘cyclic shift’ in a frequencydomain may correspond to a ‘phase shift’ in a time domain.

Where an i number of iterations is 0, the decision unit 521 makes adecision on the data using an output of the phase adjusting unit 516. Inthis case, since a portion of frequency spectrums of original data iseliminated, there may be a corruption in data where a decision is made.Such corrupted data may be recovered as the i number of iterationincreases.

That is, the inverse cyclic shifter 517 cyclic shifts {Y_(K)} up tod_(o) number of times in an inverse direction of the frequency spectrumsof data and the pilots are cyclic-shifted. As an example, wherefrequency spectrums and pilots are left cyclic-shifted, the inversecyclic shifter 517 right cyclic-shifts {Y_(K)} up to d_(o) number oftimes.

The second DFT 520 re-transforms an output {{tilde over (s)}_(n)} of thedecision unit 521 into a frequency domain signal.

The adder 518 provides the second DFT 519 with a signal {{tilde over(S)}_(k)} which is generated by adding an output of the inverse cyclicshifter 517 to an output of the second DFT 519.

The second DFT 519 re-provides the decision unit 521 with an output ofthe second DFT 519, and the decision unit 521 restores a corruptedportion of the data.

FIG. 6 illustrates a method for transmitting a signal for performingfrequency domain equalization according to an exemplary embodiment.

In operation S610, positions for inserting pilots in a frequency domainare determined based on frequency spectrums of data.

In operation S620, the pilots are inserted between the frequencyspectrums of the data according to the determined positions forinserting pilots.

In operation S630, the frequency spectrums of the data and the insertedpilots are transformed to a time domain signal.

Although not illustrated in FIG. 6, the method may further comprise anoperation of cyclic-shifting the frequency spectrums of the data and theinserted pilots so that at least one target pilot of the pilots existsin a predetermined position.

According to certain embodiments described above, a transmitter maytransmit pilots to a receiver without deteriorating efficiency of afrequency.

According to certain embodiments described above, a receiver mayeffectively locate positions of pilots without additionally receivinginformation regarding the positions of the pilots.

According to certain embodiments described above, distortion ofdata/signal may be minimized.

The above-described methods including an exemplary signal transmissionmethod for performing frequency domain equalization may be recorded, orfixed in one or more computer-readable media that includes programinstructions to be implemented by a computer to cause a processor toexecute or perform the program instructions. The media may also include,independent or in combination with the program instructions, data files,data structures, and the like. Examples of computer-readable media mayinclude magnetic media such as hard disks, floppy disks, and magnetictape; optical media such as CD ROM disks and DVD; magneto-optical mediasuch as optical disks; and hardware devices that are speciallyconfigured to store and perform program instructions, such as read-onlymemory (ROM), random access memory (RAM), flash memory, and the likeExamples of program instructions include both machine code, such asproduced by a compiler, and files containing higher level code that maybe executed by the computer using an interpreter. The described hardwaredevices may be configured to act as one or more software modules inorder to perform the methods and/or operations described above.

A number of exemplary embodiments have been described above.Nevertheless, it will be understood that various modifications may bemade. For example, suitable results may be achieved if the describedtechniques are performed in a different order and/or if components in adescribed system, architecture, device, or circuit are combined in adifferent manner and/or replaced or supplemented by other components ortheir equivalents. Accordingly, other implementations are within thescope of the following claims.

What is claimed is:
 1. A receiver for performing frequency domainequalization, the receiver comprising: a signal receiving unit whichreceives a signal transmitted from a transmitter via a channel; a firstdiscrete Fourier transformer (DFT) which transforms the received signalinto a first frequency domain signal, the first frequency domain signalincluding frequency spectrums of data and pilots; a channel estimatorwhich ascertains positions of the pilots with respect to positions ofthe frequency spectrums of the data using a channel frequency responsebeing calculated based on the pilots, and estimates a frequency responseof the channel based on the ascertained positions of the pilots; and afrequency domain equalizer which performs equalization with respect tothe first frequency domain signal based on the estimated frequencyresponse of the channel, wherein the channel estimator analyzes, in atime domain, a channel frequency response being calculated based on thedata and the channel frequency response being calculated based on thepilots to ascertain the positions of the pilots.
 2. The receiver ofclaim 1, further comprising: a detector which detects the data in a timedomain according to an iterated detecting scheme.
 3. The receiver ofclaim 2, wherein the detector comprises: an inverse discrete Fouriertransformer (IDFT) which transforms an output of the frequency domainequalizer into a time domain signal; a decision unit which makes adecision with respect to an output of the IDFT; a second DFT whichtransforms an output of the decision unit into a frequency domainsignal; and an adder which provides the IDFT with a signal beinggenerated by adding an output of the second DFT and the output of thefrequency domain equalizer.
 4. The receiver of claim 2, wherein thedetector iteratively detects the data up to a predetermined number oftimes.
 5. The receiver of claim 1, wherein the channel estimatorascertains the positions of the pilots based on a dispersion of a firsttime domain response and a dispersion of a second time domain response,and estimates the frequency response of the channel, wherein the firsttime domain response is a time domain representation of the channelfrequency response being calculated based on the data and the secondtime domain response is a time domain representation of the channelfrequency response being calculated based on the pilots.
 6. A receiverfor performing frequency domain equalization, the receiver comprising: asignal receiving unit which receives a signal transmitted from atransmitter via a channel; a first discrete Fourier transformer (DFT)which transforms the received signal into a first frequency domainsignal, the first frequency domain signal including frequency spectrumsof data and pilots, and the frequency spectrums of the data and thepilots being cyclic-shifted so that at least one target pilot of thepilots exists in a predetermined position; a frequency domain equalizerwhich estimates the channel based on the pilots and equalizes the firstfrequency domain signal based on the estimated channel; a first inversediscrete Fourier transformer (IDFT) which transforms an output of thefrequency domain equalizer into a time domain signal; a cyclic shiftdetermination unit which determines how much the frequency spectrums ofthe data and the pilots are cyclic-shifted, based on an output of thefirst IDFT; a phase adjusting unit which adjusts a phase of the outputof the first IDFT based on the determination result; and a decision unitwhich makes a decision with respect to the data using an output of thephase adjusting unit.
 7. The receiver of claim 6, further comprising: asecond DFT which transforms an output of the decision unit into afrequency domain signal; an inverse cyclic shifter which cyclic-shiftsthe output of the frequency domain equalizer as much as the frequencyspectrums of the data and the pilots have been cyclic-shifted, in aninverse direction to that of the frequency spectrums of the data and thepilots; an adder which adds an output of the inverse cyclic shifter andan output of the second DFT; and a second IDFT which transforms anoutput of the adder into a time domain signal and provides thetransformed time domain signal to the decision unit.